The present invention relates to a water-based coating composition to form an infrared absorbing layer, an infrared absorbing film obtained by coating the composition on a substrate and drying it to form the infrared absorbing layer, and an imaging material or photothermographic material by the use thereof.
In imaging materials forming images through light, there is known a fact that when exposed to light, incident light is reflected or refracted on the surface or interlayer surface of the imaging material, or on the phase separation interface within the imaging material, thereby forming a blurred image and leading to deteriorated sharpness. To prevent this, so-called anti-halation dyes (hereinafter, also denoted as AH dyes) and anti-irradiation dyes (hereinafter, also denoted as AI dyes) are broadly employed.
The recent digitalization trend results in image formation using laser light. For example, infrared lasers are used as a light source of a laser image for medical use or an image setter for use in graphic arts. As an imaging material used as an output of the foregoing are employed photothermographic materials, in which infrared absorbing compounds are used as an AH dye or AI dye.
Representative examples of the infrared absorbing compounds include organic dyes and it is well known that cyanine dyes, oxonol dyes, squalelium dyes, thiopyryliumcroconium dyes, pyryliumcroconium dyes and polymethine dyes are used in the photothermographic material. These infrared absorbing compounds include a lipophilic compound and a water-soluble compound. In the case of the lipophilic compound, a hydrophobic binder is used as a binder and in the case of the water-soluble compound is used a water-soluble binder or a latex of a hydrophilic binder dispersed in water. However, in the former case, organic solvents are used as a solvent, so that a large amount of industrial investments such as a solvent recovery equipment are needed in consideration of the environment. In the latter case, on the other hand, water-based coating and drying are feasible and advantageous in environmental concerns, however, the use of a water-soluble dye produces problems with respect to water resistance of the infrared absorbing dye. Examples of a means for enabling water-based coating and drying and for providing water resistance include a method in which an aqueous dispersion comprised of finely pulverized solid lipophilic dye particles dispersed in water is coated to form an infrared absorbing layer. However, the solid dye particle dispersion produces a broader absorption band, compared to being dissolved in an organic solvent, making it difficult to form an infrared absorbing layer having desired absorption wavelengths and the desired hardness. Therefore, there is desired a water-based coating composition which enables conducting water-based coating and drying and to form an infrared absorbing layer having desired absorption wavelengths and desired hardness, and an imaging material by the use thereof.
Accordingly, it is an object of the invention to provide an infrared absorbing film in which an infrared absorbing layer can be formed by water-based coating and the formed infrared absorbing layer has enhanced water resistance and hardness and exhibits absorption similar to that of the dye dissolved in a solvent, and an imaging material or photothermographic material by the use thereof.
The foregoing object of the invention can be accomplished by the following constitution:
1. A water-based coating composition comprising a latex impregnated with an infrared absorbing compound and a water-soluble polyester;
2. A water-based coating composition comprising a latex impregnated with an infrared absorbing compound and a latex comprised of an active methylene group-containing polymer;